From the plaque:
On August 5, 1775, the Spanish
packet San Carlos, under the command of Lieutenant Juan
Manuel de Ayala, became the first ship to enter San Francisco
Bay. A month and a half was spent in surveying the bay
from its southernmost reaches to the northern end of present-day
Suisun Bay. The San Carlos departed September 18, 1775.
Plaque placed by the State Department of Parks and Recreation in cooperation with the San Francisco Twin Bicentennial, Inc., August 5, 1975.